Export of internal Abseil changes.
-- 2dcf3ec79f961d2962cdad33ac4bfbcb14126dad by Abseil Team <absl-team@google.com>: Consolidate implementations of CountLeadingZeros and add new ones for CountTrailingZeros. Internal APIs only. PiperOrigin-RevId: 209961247 -- 4f3ac87c6928dab26faff962bb18aade9383f184 by Jorg Brown <jorg@google.com>: Fix absl::CUnescape not to write to const_cast<char*>(str->data()), which does the wrong thing if the string type is copy-on-write PiperOrigin-RevId: 209957656 -- c5103067be19dc88a4c32e5306154e5e3bba4673 by Tom Manshreck <shreck@google.com>: Update comments in time library header files. PiperOrigin-RevId: 209829588 -- fe36f9b6150243d2ac88e2a892d84c565c18cd2f by Abseil Team <absl-team@google.com>: Clarifying the sample use of absl::LoadTimeZone function in the documentation. PiperOrigin-RevId: 209782218 GitOrigin-RevId: 2dcf3ec79f961d2962cdad33ac4bfbcb14126dad Change-Id: I3e2f87a8c543599b81eada58409a9bddc0b51ab8
This commit is contained in:
Abseil Team
Derek Mauro
parent
bed5bd6e18
commit
5e7d459eec
11 changed files with 345 additions and 69 deletions
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@ -427,3 +427,23 @@ cc_test(
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"@com_github_google_benchmark//:benchmark_main",
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],
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)
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cc_library(
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name = "bits",
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hdrs = ["internal/bits.h"],
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visibility = [
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"//absl:__subpackages__",
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],
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deps = [":core_headers"],
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)
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cc_test(
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name = "bits_test",
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size = "small",
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srcs = ["internal/bits_test.cc"],
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copts = ABSL_TEST_COPTS,
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deps = [
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":bits",
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"@com_google_googletest//:gtest_main",
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],
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)
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@ -31,6 +31,7 @@ list(APPEND BASE_PUBLIC_HEADERS
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list(APPEND BASE_INTERNAL_HEADERS
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"internal/atomic_hook.h"
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"internal/bits.h"
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"internal/cycleclock.h"
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"internal/direct_mmap.h"
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"internal/endian.h"
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193
absl/base/internal/bits.h
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193
absl/base/internal/bits.h
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@ -0,0 +1,193 @@
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// Copyright 2018 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#ifndef ABSL_BASE_INTERNAL_BITS_H_
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#define ABSL_BASE_INTERNAL_BITS_H_
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// This file contains bitwise ops which are implementation details of various
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// absl libraries.
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#include <cstdint>
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// Clang on Windows has __builtin_clzll; otherwise we need to use the
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// windows intrinsic functions.
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#if defined(_MSC_VER)
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#include <intrin.h>
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#if defined(_M_X64)
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#pragma intrinsic(_BitScanReverse64)
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#pragma intrinsic(_BitScanForward64)
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#endif
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#pragma intrinsic(_BitScanReverse)
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#pragma intrinsic(_BitScanForward)
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#endif
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#include "absl/base/attributes.h"
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#if defined(_MSC_VER)
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// We can achieve something similar to attribute((always_inline)) with MSVC by
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// using the __forceinline keyword, however this is not perfect. MSVC is
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// much less aggressive about inlining, and even with the __forceinline keyword.
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#define ABSL_BASE_INTERNAL_FORCEINLINE __forceinline
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#else
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// Use default attribute inline.
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#define ABSL_BASE_INTERNAL_FORCEINLINE inline ABSL_ATTRIBUTE_ALWAYS_INLINE
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#endif
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namespace absl {
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namespace base_internal {
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ABSL_BASE_INTERNAL_FORCEINLINE int CountLeadingZeros64Slow(uint64_t n) {
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int zeroes = 60;
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if (n >> 32) zeroes -= 32, n >>= 32;
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if (n >> 16) zeroes -= 16, n >>= 16;
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if (n >> 8) zeroes -= 8, n >>= 8;
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if (n >> 4) zeroes -= 4, n >>= 4;
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return "\4\3\2\2\1\1\1\1\0\0\0\0\0\0\0"[n] + zeroes;
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}
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ABSL_BASE_INTERNAL_FORCEINLINE int CountLeadingZeros64(uint64_t n) {
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#if defined(_MSC_VER) && defined(_M_X64)
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// MSVC does not have __buitin_clzll. Use _BitScanReverse64.
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unsigned long result = 0; // NOLINT(runtime/int)
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if (_BitScanReverse64(&result, n)) {
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return 63 - result;
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}
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return 64;
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#elif defined(_MSC_VER)
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// MSVC does not have __buitin_clzll. Compose two calls to _BitScanReverse
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unsigned long result = 0; // NOLINT(runtime/int)
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if ((n >> 32) && _BitScanReverse(&result, n >> 32)) {
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return 31 - result;
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}
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if (_BitScanReverse(&result, n)) {
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return 63 - result;
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}
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return 64;
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#elif defined(__GNUC__)
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// Use __builtin_clzll, which uses the following instructions:
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// x86: bsr
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// ARM64: clz
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// PPC: cntlzd
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static_assert(sizeof(unsigned long long) == sizeof(n), // NOLINT(runtime/int)
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"__builtin_clzll does not take 64-bit arg");
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// Handle 0 as a special case because __builtin_clzll(0) is undefined.
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if (n == 0) {
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return 64;
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}
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return __builtin_clzll(n);
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#else
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return CountLeadingZeros64Slow(n);
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#endif
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}
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ABSL_BASE_INTERNAL_FORCEINLINE int CountLeadingZeros32Slow(uint64_t n) {
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int zeroes = 28;
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if (n >> 16) zeroes -= 16, n >>= 16;
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if (n >> 8) zeroes -= 8, n >>= 8;
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if (n >> 4) zeroes -= 4, n >>= 4;
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return "\4\3\2\2\1\1\1\1\0\0\0\0\0\0\0"[n] + zeroes;
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}
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ABSL_BASE_INTERNAL_FORCEINLINE int CountLeadingZeros32(uint32_t n) {
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#if defined(_MSC_VER)
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unsigned long result = 0; // NOLINT(runtime/int)
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if (_BitScanReverse(&result, n)) {
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return 31 - result;
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}
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return 32;
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#elif defined(__GNUC__)
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// Use __builtin_clz, which uses the following instructions:
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// x86: bsr
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// ARM64: clz
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// PPC: cntlzd
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static_assert(sizeof(int) == sizeof(n),
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"__builtin_clz does not take 32-bit arg");
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// Handle 0 as a special case because __builtin_clz(0) is undefined.
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if (n == 0) {
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return 32;
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}
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return __builtin_clz(n);
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#else
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return CountLeadingZeros32Slow(n);
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#endif
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}
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ABSL_BASE_INTERNAL_FORCEINLINE int CountTrailingZerosNonZero64Slow(uint64_t n) {
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int c = 63;
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n &= ~n + 1;
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if (n & 0x00000000FFFFFFFF) c -= 32;
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if (n & 0x0000FFFF0000FFFF) c -= 16;
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if (n & 0x00FF00FF00FF00FF) c -= 8;
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if (n & 0x0F0F0F0F0F0F0F0F) c -= 4;
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if (n & 0x3333333333333333) c -= 2;
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if (n & 0x5555555555555555) c -= 1;
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return c;
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}
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ABSL_BASE_INTERNAL_FORCEINLINE int CountTrailingZerosNonZero64(uint64_t n) {
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#if defined(_MSC_VER) && defined(_M_X64)
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unsigned long result = 0; // NOLINT(runtime/int)
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_BitScanForward64(&result, n);
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return result;
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#elif defined(_MSC_VER)
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unsigned long result = 0; // NOLINT(runtime/int)
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if (static_cast<uint32_t>(n) == 0) {
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_BitScanForward(&result, n >> 32);
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return result + 32;
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}
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_BitScanForward(&result, n);
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return result;
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#elif defined(__GNUC__)
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static_assert(sizeof(unsigned long long) == sizeof(n), // NOLINT(runtime/int)
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"__builtin_ctzll does not take 64-bit arg");
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return __builtin_ctzll(n);
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#else
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return CountTrailingZerosNonZero64Slow(n);
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#endif
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}
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ABSL_BASE_INTERNAL_FORCEINLINE int CountTrailingZerosNonZero32Slow(uint32_t n) {
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int c = 31;
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n &= ~n + 1;
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if (n & 0x0000FFFF) c -= 16;
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if (n & 0x00FF00FF) c -= 8;
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if (n & 0x0F0F0F0F) c -= 4;
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if (n & 0x33333333) c -= 2;
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if (n & 0x55555555) c -= 1;
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return c;
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}
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ABSL_BASE_INTERNAL_FORCEINLINE int CountTrailingZerosNonZero32(uint32_t n) {
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#if defined(_MSC_VER)
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unsigned long result = 0; // NOLINT(runtime/int)
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_BitScanForward(&result, n);
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return result;
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#elif defined(__GNUC__)
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static_assert(sizeof(int) == sizeof(n),
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"__builtin_ctz does not take 32-bit arg");
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return __builtin_ctz(n);
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#else
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return CountTrailingZerosNonZero32Slow(n);
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#endif
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}
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#undef ABSL_BASE_INTERNAL_FORCEINLINE
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} // namespace base_internal
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} // namespace absl
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#endif // ABSL_BASE_INTERNAL_BITS_H_
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97
absl/base/internal/bits_test.cc
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97
absl/base/internal/bits_test.cc
Normal file
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@ -0,0 +1,97 @@
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// Copyright 2018 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include "absl/base/internal/bits.h"
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#include "gtest/gtest.h"
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namespace {
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int CLZ64(uint64_t n) {
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int fast = absl::base_internal::CountLeadingZeros64(n);
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int slow = absl::base_internal::CountLeadingZeros64Slow(n);
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EXPECT_EQ(fast, slow) << n;
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return fast;
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}
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TEST(BitsTest, CountLeadingZeros64) {
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EXPECT_EQ(64, CLZ64(uint64_t{}));
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EXPECT_EQ(0, CLZ64(~uint64_t{}));
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for (int index = 0; index < 64; index++) {
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uint64_t x = static_cast<uint64_t>(1) << index;
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const auto cnt = 63 - index;
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ASSERT_EQ(cnt, CLZ64(x)) << index;
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ASSERT_EQ(cnt, CLZ64(x + x - 1)) << index;
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}
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}
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int CLZ32(uint32_t n) {
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int fast = absl::base_internal::CountLeadingZeros32(n);
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int slow = absl::base_internal::CountLeadingZeros32Slow(n);
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EXPECT_EQ(fast, slow) << n;
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return fast;
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}
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TEST(BitsTest, CountLeadingZeros32) {
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EXPECT_EQ(32, CLZ32(uint32_t{}));
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EXPECT_EQ(0, CLZ32(~uint32_t{}));
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for (int index = 0; index < 32; index++) {
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uint32_t x = static_cast<uint32_t>(1) << index;
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const auto cnt = 31 - index;
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ASSERT_EQ(cnt, CLZ32(x)) << index;
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ASSERT_EQ(cnt, CLZ32(x + x - 1)) << index;
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ASSERT_EQ(CLZ64(x), CLZ32(x) + 32);
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}
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}
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int CTZ64(uint64_t n) {
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int fast = absl::base_internal::CountTrailingZerosNonZero64(n);
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int slow = absl::base_internal::CountTrailingZerosNonZero64Slow(n);
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EXPECT_EQ(fast, slow) << n;
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return fast;
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}
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TEST(BitsTest, CountTrailingZerosNonZero64) {
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EXPECT_EQ(0, CTZ64(~uint64_t{}));
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for (int index = 0; index < 64; index++) {
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uint64_t x = static_cast<uint64_t>(1) << index;
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const auto cnt = index;
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ASSERT_EQ(cnt, CTZ64(x)) << index;
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ASSERT_EQ(cnt, CTZ64(~(x - 1))) << index;
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}
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}
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int CTZ32(uint32_t n) {
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int fast = absl::base_internal::CountTrailingZerosNonZero32(n);
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int slow = absl::base_internal::CountTrailingZerosNonZero32Slow(n);
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EXPECT_EQ(fast, slow) << n;
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return fast;
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}
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TEST(BitsTest, CountTrailingZerosNonZero32) {
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EXPECT_EQ(0, CTZ32(~uint32_t{}));
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for (int index = 0; index < 32; index++) {
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uint32_t x = static_cast<uint32_t>(1) << index;
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const auto cnt = index;
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ASSERT_EQ(cnt, CTZ32(x)) << index;
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ASSERT_EQ(cnt, CTZ32(~(x - 1))) << index;
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}
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}
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} // namespace
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